Rule of thumb in evaluating gear mesh 


A quick guide on gear tooth clearance;



No blood = too loose.

Aircraft Mechanic passes out = too tight.

Moderate bleeding = acceptable clearance.


Note to builders: When turning engine over by gripping flywheel, avoid the 10 and 2 O’clock grip because it puts the right thumb very close to the point where the starter and ring gear mesh. Proper mesh clearance is set with a 1/16″ drill in in a separate operation, thumb is not an accepted substitute for 1/16″ drill.



About William Wynne
I have been continuously building, testing and flying Corvair engines since 1989. Information, parts and components that we developed and tested are now flying on several hundred Corvair powered aircraft. I earned a Bachelor of Science in Professional Aeronautics and an A&P license from Embry-Riddle Aeronautical University, and have a proven 20 year track record of effectively teaching homebuilders how to create and fly their own Corvair powered planes. Much of this is chronicled at and in more than 50 magazine articles.

3 Responses to Rule of thumb in evaluating gear mesh 

  1. George Willenbrock, small time customer, thankful reader says:

    Was that issue of Sport Aviation OK?

  2. Bob 'early builder' Dewenter says:

    Ha! ‘rule of thumb’…I get it…

  3. Steve says:

    Do that too many more times and your thumb will be an acceptable substitute for a 1/16″ drill. Ouch. No need to replicate that experiment to validate the results.

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